1UVERS. 



RIVF.KS. 



120 



t brar ao much moisture as the districts that are regularly 

 tin., in 1 ->!, the river Xenam in Siani rose to an 

 rstreorimary height : the inundation* reached the large orchard* 

 which fr nuay milra in extent cover the more elevated tract, llonc 

 the lnk. uxl aSurd subsistence to a numerous population. Several 

 it-trree were almost dertroyrd, and fi>r some years the 

 manffuateeiM and dorian* were scarce. 



The Indus [ HIXLCM .1 belong* to both of these 



< UWM of riven, or rather to all three. The elevation of its wnt.-i - is 

 owm>; to the periodical melting of the snow and the subsequent rains, 

 and it i> tubjert also to enormous occasional inundations. In the 

 year 1*41, according to Maior < niiiin^lnni, in his work on l,idk, the 

 mas* of water accumulated, and which caused the inundation of the 

 land* bordering the lower part of its course, was estimated at 

 30.000,000,000 cubic feet, equal to a volume 100 feet deep, 380 feet 

 wide, and 100 auiat lung. A kimilar inundation, though probably of 



r magnitude, took place in August, 1858, when, at Attock, the 

 water row 50 fert in seven hours and a half, and attained 90 feet 

 during the day. Its affluent, the t'.ibul river, tovrd ajneanlt for ten 

 hour*. Valuable investigations of the mechanical philosophy of tl-^- 

 phenomena, and of the relation* between the velocity of a river-stream 

 and that of the tide or other waves to which it may be subject, by 

 Mr. J. Obbard and Archdeacon J. H. Pratt, will bo found in the 

 Journal of the Asiatic Society of Bengal,' N. S., vol. xxix. (1860, 

 i. p. 263-888. The Utter subject has important relations with 

 that of the ascent of the tide up a river, noticed below. 



All the riven between the tropics which are swollen by periodical 

 rains lie only in one hemisphere, the northern or the southern. In 

 the countries through which they flow the waters are low and the 

 ground dry dining part of the year, so as to admit of easy cultivation, 

 ad at another snesnn the fields are fertilised by the inundations. The 

 Nile and the Auiaconas are alone exceptions. Though the course of 

 the latter river is in the southern hemisphere, its affluents extend far 

 to the north and south, into both hemispheres, and probably three- 

 fourths of the tropical rains which descend upon South America find 

 their way to that large river. To this circumstance are owing its 

 immense volume of water and its great depth. The Amazonas, 

 properly speaking, is never at its lowest level, in the sense in which 

 that term is applied to other riven. When the northern rivers cease 

 to bring down the supply which is owing to the periodical rains, the 

 southern begin to bring their contributions. This fact seems suffi- 

 ciently to explain the immense tracts of alluvial soil which extend 

 along the river to a great distance, but the same circumstance also 

 keeps the soil in a state of continual moisture, and makes it a per- 

 petual Kwamp. Accordingly we find that the banks of that river, 

 which admits of a more extensive navigation than any other river in 

 the world, remain nearly destitute of agricultural settlement-, and are 

 (till in the pnastssino of savage tribes. In the northern portion of the 

 upper course of the Nile, that river appears to be almost stagnant 

 except during the rains, and to consist in the dry season of a aeries of 

 swamps and lakes, rather than to form a continuous stream. 



The rivers which drain the countries between 30" N. latitude and 

 tho*e in which the mean temperature of the winter season does not 

 rise above SO", are subject to occasional inundations. But these over- 

 flowings occur only in those rivers whose upper course lies within 

 mountain-range* which are covered with snow for a considerable part 

 of the year. In such cases, while the snow covers the more elevated 

 portion of the mountain-ranges, a sudden change in the weather, which 

 produces a warm wind, bring* great volumes of vapours, which, falling 

 in abundant rain, soon dinaolve the snow, and the mountain-streams 



.-wn their water* with increased volume and velocity. As soon 

 as the waters reach a level tract, it is inundated. As these inundations 



take place unexpectedly, they cause great damage. Thus we find 

 that some valleys in the Ozark Mountains, in the United States of North 

 America, are almost uninhabitable, owing to the sudden inundations 

 to which the rivers of that mountain-region are subject. Many rivers 

 however never inundate the adjacent country, unless a heavy gale of 

 wind should blow directly up the river, and drive the sea into it with 

 great force. Such inundations are very sudden, and sometime* also 

 extensive, but they arc of short duration. [CLI1IATK : RAIN.] 



An important subject in the history of rivers, relating to the dis- 

 tribution of temperature within certain areas of the earth's surface 

 and the immediately incumbent atmosphere, and their equalisation in 

 others, and which bears also on the connection of rivers with the 

 welfare of organic nature and the human race, is the variation of th.-ir 

 temperature in different part* of their course, both at the same and at 

 different seasons. This depends, proximately, on the temperature of 

 their affluents, and may even give information of the physical utate of 

 the countries in which they rine, when these are otherwise unknown. 

 Dr. Joseph I). Hooker, in his ' Himalayan Journals' (voL ii., p. 80), 

 has given some interesting facts on this point, as presented by the 

 rirers which rise in the Sikkiiu Himalaya. The Teesta, a tributary of 

 *" Mgn. or Brahmaputra, is always cool in summer (where its bed 

 ( below 2000 feet in absolute elevation), its temperature being 20 

 Mow that of the air ; whereas, in mill-winter, when there is less cloud 

 the snows are not melting, it ia only a few degree* colder than the 



At Hhoomsong, of which tlin elevation w 15cm fret, the mean 

 temperature of the Teota, in that season, was 61", and that of the air 



r.'2-S; at. that elevation the temperature of the water rarely exceeds 

 C0 at midsummer. Between the altitudes of 4000 feet and 300 (the 

 plains of India) its mean temperature varies about 10 lietwe<-ii January 

 ;,!! .Inly; at oOcm feet it varies from 65" to 43 during the same 

 |H-riod ; and at 10,000 feet it freezes at the edges in winter, au- 

 to 50 in July. In June, in descending from 12,000 to 1000 feet, Dr. 

 Hooker found that its temperature did not rise 10, while that of the 

 air rose 80 or 40. The temperature of the northern feeders . 

 liver, in sonu- parts of their course, actually rises with the increasing 

 elevation. Thus, the Zemu, during the traveller's stay at its junction 

 with the Thlonok (which Ins its source in the north-east snowy flank 

 of Kiiieliinjnnga, one of the three or four highest mountains in the. 

 world* was at 40", or 6 wanner than the latter ; at 1100 feet higher 

 IN, and at 1100 feet higher still it was 49. " These observa- 

 tions," l)r. Hooker adds, " were repeated in different weeks, and several 

 times on the same day, both in ascending and descending, and always 

 with the same result : they told, as certainly as if I had followed the 

 river to its source, that it rose in a drier and comparatively sunny 

 climate, and flowed among little snowed mountains." Another explorer 

 of nature, Mr. Alfred R. Wallace, has recorded (' Travels on the Amazon 

 and liio Negro,' p. 431) some facts apparently of the same description, 

 not, however, observed by himself, and which he professes his inability 

 to account for. In the month of May some very cold days are said to 

 occur annually on the Upper Amazon and Hio Negro, sometimes so 

 severe that the inhabitants suffer much, and the fishes in the rivers 

 even die of the cold ; though five or ten degrees of diminution of tem- 

 perature, Mr. Wallace remarks, is as much as ever takes place. We 

 conceive the depression of temperature of the local atmosphere affecting 

 the inhabitants to be occasioned by the air brought down in contact 

 with the cooled water of the rivers, the temperature of which must 

 be still lower, and that the cause is the annual melting of the snows 

 about the sources of some of their head-streams. 



In adverting to the advantages which a country derives from its 

 rivers, we must first observe that the water is extensively used for the 

 purposes of domestic economy. It is much purer than that of wells ; 

 for river water in general contains much less saline matter than spring- 

 water ; it has also earthy particles in suspension, which may easily be 

 separated by filtration, and which are deposited as a sediment when 

 the water is left to stand for a short time. The water of wells 

 generally contains a small quantity of some mineral salts in solution. 

 The water of rivers is used, and is nearly equal to rain water, for all 

 domestic purposes. The upper courses of rivers are generally inhabited 

 by a small number of species of fish, and the whole amount is not 

 great. But towards their mouths the number both of species and 

 individuals increases. The importance of a river fishery may be esti- 

 mated when we consider the quantity of salmon which is taken in the 

 rivers of Britain, or of the beluga and sturgeon which is caught in the 

 neighbourhood of Astrakhan. Many rivers, which are not adapted to 

 the purposes of navigation, are converted into powerful instruments 

 for assisting the industry of a country by the moving-power which 

 they supply for mills and other heavy machinery. The advantage of 

 such a natural moving-power primarily determines the seat of manu- 

 factures, as was the case in South Lancashire, where this advantage is 

 combined with abundance of coal. The Atlantic States of North 

 America are generally provided with abundance of streams, a circum- 

 stance which favours the establishment of manufactures. 



The greatest advantages however which a country derives from its 

 rivers are the facilities which they supply for conveying the produce 

 of agriculture and of manufacturing industry to distant parts at a 

 moderate expense. In this respect the rivers may be compared to 

 the arteries and veins of the human body, which diffuse life and 

 strength through all parts. Navigable rivers vivify, maintain, and 

 excite the efforts of human industry. In many countries, where roads 

 are neglected, it is estimated that the transport of goods by land is four 

 times as expensive as that by means of navigable rivers, and thus 

 many heavy and bulky commodities could not be brought to market 

 but for the cheap conveyance of rivers. In considering the capacity of 

 a river for navigation, two circumstances mainly require notice how 

 far seafaring vessels may ascend, and how far the river is navigable for 

 river boats. 



s, -.(faring vessels can ascend many rivers as far as the tides extend. 

 Indeed some rivers, as the Amazonas, may be navigated by large vessels 

 to a much greater distance than the tide ascends, but in others tin- 

 waters become shallow long before the limit of tide-water is reached. 

 Still high tides facilitate the navigation of rivers by large vessels, not 

 only by producing a current contrary to that of the river, but also by 

 temporarily increasing the depth of water so that vessels can jmss over 

 shallows and sandlxmks, which at low tides are nearly or quite dry. 

 This is frequently the case in rivers where the tides rise more than 1 2 

 feet. The tides in rivers are not of equal duration, as is the case in 

 most parts of the sea ; but the ebb tides frequently last twice as long 

 a the flowing tides. At Rotterdam the tides flow for about 4 hours 

 and 5 minutes, but the ebb lasts 7 hours and 55 minutes. The Meer- 

 wede at Dordrecht flows against the current of the river for 3 hours 

 and 51 minutes, and with it 8 hours and 9 minutes. This difference is 

 easily explained, when the force of the river current is taken into 

 account. The same circumstance explains the difference in the 

 velocity of the ebbing and flowing tide. Between the North Sea and 



